Problems and Opportunities in the Design of Entrances to Ports and Harbors Proceedings of a Symposium (1981) / Chapter Skim
Currently Skimming:
Ship Controllability
Ship Controllability
Pages 75-94
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 75... ...
Although the quantification of ship controllability will differ for each case to be considered, the method will always be based on operational research involving statistical descriptions of systems. The results of such studies provide the possibility of performing risk analysis.
|
From page 76... ...
n Separate consideration of the inherent characteristics of the ship in the dual system will be indicated by the term ~maneuverability. n Since no uniform definition of ship controllability is presented in the literature, use is made here of the following description, illustrated in Figure 1: A ship is defined to be controllable when it can be handled in such a way that the deviation of the actual maneuver (described by all stated variables of the system)
|
From page 77... ...
General description of the controlled ship by means of a block diagram.
|
From page 78... ...
Such a reference value would represent controllability resulting in minimum deviation between actual and projected maneuvers, or in other words, the ship is optimally controllable when it performs maneuvers that show the closest agreement with the hypothetical maneuver designed for the waterway. In the paper by the SNAME H-10 panel, the suggestion is offered that this reference value be def ined as the n inherent controllability.
|
From page 79... ...
This compromise would fall somewhere between as wide a harbor mouth as possible for navigational purposes and as small a harbor mouth as possible to minimize wave penetration into the harbor. Exploring the waterway dimensions required to facilitate the entry of ships into the harbor, the inherent controllability will lead to a width of the approach channel dependent on the ship's drift angle against current and wind, while the dimensions of the harbor mouth and the area behind it will depend on the current shear in front of the outer piers.
|
From page 80... ...
80 outer piers inner piers at Cal ,rre . I ~ approach channe 1 ( dredged )
|
From page 81... ...
The channel width has to be 600 meters sat least, n because the initial controllability is considered to provide the minimum deviation between actual and intended maneuver. During normal operations, the ship's controllability will be less (leading to larger channel widths)
|
From page 82... ...
Initial controllability of ship in design alternative B approach channe 1 .
|
From page 83... ...
It is assumed that a harbor entrance of 500 m is acceptable from the point of view of wave penetration in the berthing area. Widening of the approach channel from the point of view of initial controllability of the ship has to be rejected.
|
From page 84... ...
approach channel 4 km :3 km outer piers inner piers 1 , , , , ~ 1 /1\ 1 2 km 1 km / i~ ·_i ._, 0 In n .. 0 o 4 km 3 km 2 km 1 km Figure 8.
|
From page 85... ...
However, in the initial stage of design, the harbor dimensions seem acceptable relative to the controllability of the ship considered when one neglects these required widths of lane, instead considering the chances of exceeding the given waterway dimensions. One then obtains the following picture: chance of exceeding dimensions of an extreme in the 500 m approach channel p = 0.015.
|
From page 86... ...
Compare approach channels, both 300 meters wide, to two different ports, A and B For port A, the width of lane is required to be 290 meters for ships of different types while port B is designed for a specific type of ship for which a lane 200 meters wide is required.
|
From page 87... ...
Example 1. It was seen in the previous section that in zero-current conditions the required width of lane in the approach channel changed from 290 m to 600 m when the width of the port entrance changed from 500 m to 300 m.
|
From page 88... ...
Little gain in controllability can be achieved by widening the opening' Example 2. It was seen in the previous section that for the design concept A, the required width of lane in the approach channel changed from 290 meters when there was zero current to 620 meters when the ship had to sail in a variety of crosscurrents with a maximum speed of 3 knots.
|
From page 89... ...
_ Aw /w a a Ac/c 1 -__ 1 , , , 1 O kn 1 kn 2 kn current velocity Figure 9: Schematic indication of reduction of the sensitivity to current.
|
From page 90... ...
However, when the information to the pilot about the magnitude of the peak current is less exact, then the required width of lane increases to: 410 m at an accuracy of 87% 670 m at an accuracy of 75% One thus finds: sad= 60/350 = 1.32 for 100% accuracy 13/100 sad= 320/410= 2.72 for 87% accuracy 25/87 sad= 260/670= 2.42 for 75% accuracy 12/75 in which: Sal = sensitivity to accuracy of information. From the above results it can be concluded that the navigability of a 350-meter-wide waterway with 100 percent accuracy of information about the current is better than the navigability of a 670-meter-wide waterway in which the accuracy of information about the current is 75 percent, while this latter design offers better navigability than a 450-meter-wide waterway in which the accuracy of current information is 87 percent.
|
From page 91... ...
The problem to date has been the inability to derive a systematic evaluation process that correctly considers all the complex interactive elements that contribute to the occurrence and activation of hazards; namely, The ship's inherent hydrodynamic characteristics, The ~skill" of the mariner in controlling the ship, The peripheral aids (either on board or external to the ship) that furnish data or control to the mariner, and The effects of a particular environment (port geophysics, wind, current, channel width and depth, other vessels, etc.)
|
From page 92... ...
F et al., Realtime Simulation of Tanker Operations for the Trans Alaska Pipeline System, n Paper presented at Annual Meeting of The Society of Naval Architects and Marine Engineers, New York, 1977.
|
From page 93... ...
11. Panel H-10 of The Society of Naval Architects and Marine Engineers, "Proposed Procedures for Determining Ship Controllability Requirements and Capabilities, n Paper presented at S.T.A.R.
|
From page 94... ...
Your presentation highlights the integration of ship maneuverability or controllability with harbor design: the system also needs hazard" analysis, failure mode and effects analysis. CRANE: I'm fully in accord with full systems analysis.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.